1. Field of the Invention The present invention relates to optical communications devices and, more particularly, to an optical semiconductor module for optical amplification application.
2. Description of the Related Art
In general, an optical amplifier for use in optical communications is mainly divided into an optical-fiber amplifier and a semiconductor optical amplifier (SOA). An example of the optical-fiber amplifiers is erbium-doped optical-fiber amplifier (EDFA), in which a light source is pumped into an erbium-doped optical fiber so that the inputted optical signals are amplified through stimulated emission by the erbium element. In contrast, a commonly used semiconductor optical amplifier consists of layered structures formed on a semiconductor substrate in sequence, including an active layer with a multiple (or single) quantum well structure for a fiber amplification, a waveguide layer operable as a broadcast media of the inputted optical signals, a clad layer that encompasses the waveguide layer to confine the inputted optical signals therein, an upper electrode layer, and a lower electrode layer. It is well known that the semiconductor optical amplifier is more advantageous in that the level of the current applied to the upper electrode layer can be adjusted as occasion demands.
However, it is important to maintain a constant ratio between the inputted optical signal power and the outputted optical signal power (or an optical amplification ratio) in the semiconductor optical fiber. That is to say, if the optical amplification ratio of the semiconductor optical amplifier exceeds a threshold value, it can have a bad influence on the operation of other optical elements that are connected to the semiconductor optical amplifier. In addition, if the optical-amplification ratio of the semiconductor optical amplifier is smaller than the threshold value, it can deteriorate the characteristics of the outputted optical signals, such as the signal-to-noise ratio. As a result, a monitoring device is typically employed to ensure that optical characteristics are not affected by a discrepancy in the optical-amplification ratio.
FIG. 1 shows a monitoring device of a semiconductor optical amplifier according to the related art. As shown in FIG. 1, the monitoring device includes a semiconductor optical amplifier 110, a bean splitter 129, an optical detector 130, an analog/digital converter (ADC) 140, a bias circuit 150, a digital/analog converter (DAC) 160, and a controller 170.
The semiconductor optical amplifier 110 amplifies the inputted optical signals within a designated optical-amplification ratio, and outputs the amplified optical signals.
In operation, the beam splitter 120 splits a portion of the optical signals corresponding to x % of the total optical power outputted from the semiconductor optical amplifier 110 (hereinafter referred to as an optical signal sample), then outputs the optical signal sample to the optical detector 130. The other optical signal outputs corresponding to (100xe2x88x92x) % power are passed through the beam splitter 120. Meanwhile, the optical detector 130 converts the inputted optical-signal sample from the beam splitter 120 to electric signals and outputs the corresponding electric signals. The analog/digital converter 140 converts the output signals from the optical detector 130 to corresponding digital signals and outputs the converted digital signals to the controller 170. The controller 170 determines the power of the amplified optical signal that is outputted from the semiconductor optical amplifier 110 based on the digital signal outputs from the converter 140. In particular, the controller 170 obtains a difference between the amplified optical signal""s power and a predetermined power threshold level, then adjusts the current level that is applied to the semiconductor optical amplifier 110 to adjust the optical amplification ratio of the semiconductor optical amplifier 110. Accordingly, the controller 170 outputs a control signal indicative of the adjusted current level to the digital/analog converter 160, which then converts the control signal to an analog signal and outputs the converted analog signal to the bias circuit 150. Finally, the bias circuit 150 applies the current responsive to the control signal to the semiconductor optical amplifier 110 to adjust the gain of the semiconductor optical amplifier 110. This change in the gain causes the optical amplification ratio of the semiconductor optical amplifier 110 to change. Accordingly, the controller 170 can control the optical-amplification ratio of the semiconductor optical amplifier 110 to maintain at a specific level.
There are some drawbacks in the prior art monitoring device in that it requires extra components, such as a beam splitter 120 for monitoring the outputted optical signal""s power. As a result, it increases manufacturing costs. In addition, the semiconductor optical amplifier 110, the beam splitter 120, and the optical detector 130 must be positioned precisely in an array, and further require other devices (not shown) for the same application. Furthermore, the maximum output power of the semiconductor optical amplifier 110 suffers as a portion of the outputted optical signals are extracted during the monitoring operation.
In summary, the conventional structure of the semiconductor optical amplifier module that is mounted with the semiconductor optical amplifier and the monitoring device in a housing has drawbacks associated with high manufacturing cost, low integration due to the deployment of the beam splitter and additional optical components, and a loss in the maximum output power.
The present invention overcomes the above-described problems, and provides additional advantages by providing a semiconductor optical amplifier module with a monitoring device that has a low manufacturing cost, a high integration capability, and a maximum output power.
According to an aspect of the invention, there is provided a semiconductor optical amplifier with a monitoring device, which includes: a housing having a window on both sides of opposite walls for forming a path of a first optical fiber and a second optical fiber, respectively; a semiconductor optical amplifier fixated in the housing for amplifying the inputted optical signals and outputting the amplified optical signals; a first supporter for supporting the first optical fiber; and, a second supporter for supporting the second optical fiber.
According to another aspect of the invention, the semiconductor optical amplifier further includes a first optical detector that is arrayed in such a way to detect the non-coupled light generated in the line of the first optical fiber.
The foregoing and other features and advantages of the invention will be apparent from the following, more detailed description of preferred embodiments as illustrated in the accompanying drawings in which reference characters refer to the same parts throughout the various views. The drawings are not necessarily to scale, the emphasis instead is placed upon illustrating the principles of the invention.